1. Field of the Invention
The present invention relates to imaging lenses suitable for use in photographic cameras, video cameras, electronic still cameras, etc., and more particularly, to an imaging lens capable of performing a close-distance imaging (macro imaging) operation in which an imaging magnification is about 1 and optically correcting image blur caused by hand movements or the like.
2. Description of the Related Art
A macro lens is an example of an imaging lens which is mainly used for close-distance imaging operation in which an imaging magnification is about 1. The macro lens is capable of taking an image of an object in the distance range from infinity to a close distance at which the imaging magnification is about 1, and is designed such that high optical performance is provided in the process of taking, in particular, an image of a close object (macro imaging operation).
In an imaging lens including the macro lens, variations in aberrations caused during focusing generally increase and the optical performance is degraded as the imaging magnification increases. To prevent this, the imaging lens may use a floating method in which the aberrations are corrected by moving a plurality of lens units in a process of focusing on a close object.
In the case where focusing is performed by moving a first lens unit, which is closest to the object side in the imaging lens, toward the object side, a working distance, which is a distance between the object and a lens surface closest to the object side in the first lens unit, decreases. Accordingly, an inner-focus macro lens in which focusing is performed by moving a lens unit close to the image side without moving the first lens unit has been proposed (Japanese Patent Laid-Open No. 2003-329919).
In addition, a macro lens including a part which can be moved in a direction having a component that is perpendicular to an optical axis so as to correct the image blur by shifting the image position has been proposed (Japanese Patent Laid-Open No. 2000-214380).
The close-distance imaging operation is generally performed while the size of the aperture in the aperture stop is reduced (the F-number is increased) to ensure the depth of field. However, if the size of the aperture in the aperture stop is reduced, the shutter speed is also reduced and motion blur easily occurs in the imaging operation. In addition, the influence of hand movements on the obtained image increases as the object distance decreases.